The lacrimal canaliculi (: canaliculus) are the small channels in each

eyelid An eyelid ( ) is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. "Palpebral ...

that drain lacrimal fluid, from the lacrimal puncta to the

lacrimal sac The lacrimal sac or lachrymal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla. It connects the lacrimal canaliculi, which drain tears from th ...

. This forms part of the

lacrimal apparatus The lacrimal apparatus is the physiological system containing the Orbit (anatomy), orbital structures for tears, tear production and drainage.Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Co ...

that drains lacrimal fluid from the surface of the eye to the nasal cavity.

Structure

There is a single lacrimal canaliculus in each

, a superior lacrimal canaliculus in the upper eyelid and an inferior lacrimal canaliculus in the lower eyelid. The canaliculi travel vertically and then turn medially to travel towards the lacrimal sac. At the bend, the canaliculus is dilated and called the ampulla. Usually, the superior and inferior lacrimal canaliculi join to form a common passage that enters the lateral wall of the lacrimal sac.

Superior lacrimal canaliculus

The superior lacrimal canaliculus is located in the upper eyelid. It first ascends, then bends medially towards the lacrimal sac. It drains lacrimal fluid from the superior lacrimal punctum. It is smaller and shorter than the inferior lacrimal canaliculus.

Inferior lacrimal canaliculus

The inferior lacrimal canaliculus is located in the lower eyelid. It first descends, then bends medially towards the lacrimal sac. It drains lacrimal fluid from the inferior lacrimal punctum.

Histology

The lacrimal canaliculi have a mucosa composed of a non-keratinized

stratified squamous epithelium A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural ...

on a basement membrane and a highly elastic

lamina propria The lamina propria is a thin layer of connective tissue that forms part of the moist linings known as mucous membranes or mucosae, which line various tubes in the body, such as the respiratory tract, the gastrointestinal tract, and the urogenital ...

. Surrounding the mucosa are skeletal muscle fibres continuous with the

orbicularis oculi The orbicularis oculi is a sphincter-like muscle in the face that closes the eyelids. It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and b ...

which forms a sort of sphincter. This may facilitate the draining of lacrimal fluid during blinking.

Clinical significance

Canaliculitis is inflammation of the lacrimal canaliculus.

References

{{Authority control Human eye anatomy